According to http://www.cplusplus.com/reference/string/string/operator=/, the std::string move assignment operator should be noexcept. #include <string> static_assert (std::is_nothrow_move_assignable <std::string>::value, "failed");
I'll fix this asap, very simple to do, but note that until we break the ABI basic_string will remain nonconforming in many serious ways.
As a matter of fact, isn't, in our current implementation, because std::swap itself isn't in case the allocators are not equal. I can preliminarily adjust it for ext/vstring.h (a preview of the future c++11 conforming basic_string) but it still needs work as regards the C++11 memory allocation model.
Similar to containers the move-assignment operator of basic_string should not be noexcept, because they have a narrow contract. The fact that the specification currently requires this, is a defect. This is http://cplusplus.github.io/LWG/lwg-active.html#2063
Thanks Daniel. I knew that we would have to revisit this anyway when the C++11 allocator model is implemented for the C++11 conforming basic_string. All in all, I guess better suspending this for the time being. Since, as-is, the move assignment of ext/vstring is in fact noexcept, we may want to declare it as such however. By the way, I seem to remember that Jon has work almost ready for the C++11 conformance of it.
Author: glisse Date: Fri Sep 20 15:50:09 2013 New Revision: 202781 URL: http://gcc.gnu.org/viewcvs?rev=202781&root=gcc&view=rev Log: 2013-09-20 Marc Glisse <marc.glisse@inria.fr> PR libstdc++/58338 * include/bits/allocator.h (__alloc_swap::_S_do_it, __shrink_to_fit_aux::_S_do_it): Mark as noexcept. * include/bits/basic_string.h (basic_string::_Rep) [_S_empty_rep, _M_is_leaked, _M_is_shared, _M_set_leaked, _M_set_sharable, _M_set_length_and_sharable, _M_dispose]: Likewise. (basic_string::_Alloc_hider::_Alloc_hider): Likewise. (basic_string) [_M_data, _M_rep, _M_ibegin, _M_iend, _M_limit, _M_disjunct, _M_copy, _M_move, _M_assign, _S_copy_chars, _S_compare, _S_empty_rep, shrink_to_fit, operator[] const, front const, back const]: Likewise. [clear]: Link to PR 56166. [swap]: Link to PR 58265. * include/bits/stl_deque.h (_Deque_iterator) [_S_buffer_size, _Deque_iterator, _M_const_cast, operator*, operator->, operator++, operator--, operator+=, operator+, operator-=, operator-, operator[], _M_set_node]: Mark as noexcept. (operator==(const _Deque_iterator&, const _Deque_iterator&), operator!=(const _Deque_iterator&, const _Deque_iterator&), operator<(const _Deque_iterator&, const _Deque_iterator&), operator>(const _Deque_iterator&, const _Deque_iterator&), operator<=(const _Deque_iterator&, const _Deque_iterator&), operator>=(const _Deque_iterator&, const _Deque_iterator&), operator-(const _Deque_iterator&, const _Deque_iterator&), operator+(ptrdiff_t, const _Deque_iterator&)): Likewise. (_Deque_base) [_Deque_base(const allocator_type&)]: Add missing call to _M_initialize_map. [~_Deque_base, _M_deallocate_node, _M_deallocate_map, _M_destroy_nodes]: Mark as noexcept. (_Deque_base::_Deque_impl) [_Deque_impl(const _Tp_alloc_type&), _Deque_impl(_Tp_alloc_type&&)]: Likewise. (deque) [_S_buffer_size, operator=(deque&&), shrink_to_fit, operator[], front, back, pop_front, pop_back, swap]: Likewise. [deque(), deque(const allocator_type&)]: Merge. * include/debug/deque (deque) [operator=(deque&&), shrink_to_fit, operator[], front, back, pop_front, pop_back, swap]: Mark as noexcept. * include/profile/deque (deque) [operator=(deque&&), operator[], front, back, pop_front, pop_back, swap]: Likewise. * testsuite/23_containers/deque/requirements/dr438/assign_neg.cc: Adjust line number. * testsuite/23_containers/deque/requirements/dr438/constructor_1_neg.cc: Likewise. * testsuite/23_containers/deque/requirements/dr438/constructor_2_neg.cc: Likewise. * testsuite/23_containers/deque/requirements/dr438/insert_neg.cc: Likewise. Modified: trunk/libstdc++-v3/ChangeLog trunk/libstdc++-v3/include/bits/allocator.h trunk/libstdc++-v3/include/bits/basic_string.h trunk/libstdc++-v3/include/bits/stl_deque.h trunk/libstdc++-v3/include/debug/deque trunk/libstdc++-v3/include/profile/deque trunk/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/assign_neg.cc trunk/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_1_neg.cc trunk/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_2_neg.cc trunk/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/insert_neg.cc
Author: glisse Date: Tue Sep 24 10:07:32 2013 New Revision: 202861 URL: http://gcc.gnu.org/viewcvs?rev=202861&root=gcc&view=rev Log: 2013-09-24 Marc Glisse <marc.glisse@inria.fr> PR libstdc++/58338 PR libstdc++/56166 * include/bits/basic_string.h (basic_string) [basic_string(basic_string&&)]: Make the noexcept conditional. [operator=(basic_string&&), assign(basic_string&&)]: Link to PR 58265. [begin(), end(), rbegin(), rend(), clear]: Remove noexcept. [pop_back]: Comment on the lack of noexcept. * include/debug/string (basic_string) [basic_string(const _Allocator&), basic_string(basic_string&&), begin(), end(), rbegin(), rend(), clear, operator[](size_type), pop_back]: Comment out noexcept, until vstring replaces basic_string. Modified: trunk/libstdc++-v3/ChangeLog trunk/libstdc++-v3/include/bits/basic_string.h trunk/libstdc++-v3/include/debug/string
Wht's the status of this issue? Issue still exists in GCC 5.1. Latest wording http://cplusplus.github.io/LWG/lwg-defects.html#2063 insists on making move assignment conditionally noexcept.
I've been working on LWG2063 but forgot there was this PR for it.
Author: redi Date: Fri Sep 11 11:02:14 2015 New Revision: 227681 URL: https://gcc.gnu.org/viewcvs?rev=227681&root=gcc&view=rev Log: Implement N4258 noexcept for std::basic_string. PR libstdc++/58265 * doc/xml/manual/intro.xml: Document LWG 2063 and 2064 resolutions. * doc/html/manual/bugs.html: Regenerate. * include/bits/basic_string.h (basic_string): Implement N4258. Add correct exception-specifications and propagate allocators correctly. * include/bits/basic_string.tcc (basic_string::swap): Propagate allocators correctly. * include/debug/string (__gnu_debug::basic_string): Add correct exceptions-specifications and allcoator-extended constructors. * testsuite/21_strings/basic_string/allocator/char/copy.cc: New. * testsuite/21_strings/basic_string/allocator/char/copy_assign.cc: New. * testsuite/21_strings/basic_string/allocator/char/minimal.cc: New. * testsuite/21_strings/basic_string/allocator/char/move.cc: New. * testsuite/21_strings/basic_string/allocator/char/move_assign.cc: New. * testsuite/21_strings/basic_string/allocator/char/noexcept.cc: New. * testsuite/21_strings/basic_string/allocator/char/swap.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/copy.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/minimal.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/move.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/noexcept.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/swap.cc: New. * testsuite/util/testsuite_allocator.h (tracker_allocator): Define defaulted assignment operators. Added: trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/ trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/ trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/copy.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/copy_assign.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/minimal.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/move.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/move_assign.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/noexcept.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/swap.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/ trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/copy.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/minimal.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/move.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/noexcept.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/swap.cc Modified: trunk/libstdc++-v3/ChangeLog trunk/libstdc++-v3/doc/html/manual/bugs.html trunk/libstdc++-v3/doc/xml/manual/intro.xml trunk/libstdc++-v3/include/bits/basic_string.h trunk/libstdc++-v3/include/bits/basic_string.tcc trunk/libstdc++-v3/include/debug/string trunk/libstdc++-v3/testsuite/util/testsuite_allocator.h
Fixed on trunk.
Author: redi Date: Tue Jul 12 10:56:11 2016 New Revision: 238241 URL: https://gcc.gnu.org/viewcvs?rev=238241&root=gcc&view=rev Log: Implement N4258 noexcept for std::basic_string. Backport from mainline 2015-10-02 Jonathan Wakely <jwakely@redhat.com> * testsuite/21_strings/basic_string/allocator/char/minimal.cc: Guard explicit instantiation with check for new ABI. * testsuite/21_strings/basic_string/allocator/wchar_t/minimal.cc: Likewise. Use wchar_t as char_type. Backport from mainline 2015-09-11 Jonathan Wakely <jwakely@redhat.com> PR libstdc++/58265 * doc/xml/manual/intro.xml: Document LWG 2063 and 2064 resolutions. * doc/html/manual/bugs.html: Regenerate. * include/bits/basic_string.h (basic_string): Implement N4258. Add correct exception-specifications and propagate allocators correctly. * include/bits/basic_string.tcc (basic_string::swap): Propagate allocators correctly. * include/debug/string (__gnu_debug::basic_string): Add correct exceptions-specifications and allcoator-extended constructors. * testsuite/21_strings/basic_string/allocator/char/copy.cc: New. * testsuite/21_strings/basic_string/allocator/char/copy_assign.cc: New. * testsuite/21_strings/basic_string/allocator/char/minimal.cc: New. * testsuite/21_strings/basic_string/allocator/char/move.cc: New. * testsuite/21_strings/basic_string/allocator/char/move_assign.cc: New. * testsuite/21_strings/basic_string/allocator/char/noexcept.cc: New. * testsuite/21_strings/basic_string/allocator/char/swap.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/copy.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/minimal.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/move.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/noexcept.cc: New. * testsuite/21_strings/basic_string/allocator/wchar_t/swap.cc: New. * testsuite/util/testsuite_allocator.h (tracker_allocator): Define defaulted assignment operators. Added: branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/ branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/ branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/copy.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/copy_assign.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/minimal.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/move.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/move_assign.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/noexcept.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/swap.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/ branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/copy.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/minimal.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/move.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/noexcept.cc branches/gcc-5-branch/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/swap.cc Modified: branches/gcc-5-branch/libstdc++-v3/ChangeLog branches/gcc-5-branch/libstdc++-v3/doc/html/manual/bugs.html branches/gcc-5-branch/libstdc++-v3/doc/xml/manual/intro.xml branches/gcc-5-branch/libstdc++-v3/include/bits/basic_string.h branches/gcc-5-branch/libstdc++-v3/include/bits/basic_string.tcc branches/gcc-5-branch/libstdc++-v3/include/debug/string branches/gcc-5-branch/libstdc++-v3/testsuite/util/testsuite_allocator.h
Author: redi Date: Thu Jul 5 15:56:06 2018 New Revision: 262443 URL: https://gcc.gnu.org/viewcvs?rev=262443&root=gcc&view=rev Log: PR libstdc++/58265 implement LWG 2063 for COW strings For COW strings the default constructor does not allocate when _GLIBCXX_FULLY_DYNAMIC_STRING == 0, so can be noexcept. The move constructor and swap do not allocate when the allocators are equal, so add conditional noexcept using allocator_traits::is_always_equal. PR libstdc++/58265 * include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI] [_GLIBCXX_FULLY_DYNAMIC_STRING==0] (basic_string::basic_string()): Add GLIBCXX_NOEXCEPT. (basic_string::operator=(basic_string&&)): Add _GLIBCXX_NOEXCEPT_IF to depend on the allocator's is_always_equal property (LWG 2063). (basic_string::swap(basic_string&)): Likewise. * include/bits/basic_string.tcc [!_GLIBCXX_USE_CXX11_ABI] (basic_string::swap(basic_string&)): Likewise. * testsuite/21_strings/basic_string/allocator/char/move_assign.cc: Check is_nothrow_move_assignable. * testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc: Check is_nothrow_move_assignable. * testsuite/21_strings/basic_string/cons/char/ noexcept_move_construct.cc: Likewise. * testsuite/21_strings/basic_string/cons/wchar_t/ noexcept_move_construct.cc: Likewise. Modified: trunk/libstdc++-v3/ChangeLog trunk/libstdc++-v3/include/bits/basic_string.h trunk/libstdc++-v3/include/bits/basic_string.tcc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/move_assign.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/noexcept_move_construct.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/noexcept_move_construct.cc
Now also fixed for COW strings.
Author: redi Date: Thu Jul 5 17:03:05 2018 New Revision: 262447 URL: https://gcc.gnu.org/viewcvs?rev=262447&root=gcc&view=rev Log: PR libstdc++/58265 add noexcept to basic_string::assign(basic_string&&) PR libstdc++/58265 * include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI] (basic_string::assign(basic_string&&)): Add conditional noexcept depending on the allocator's is_always_equal property (LWG 2063). * testsuite/21_strings/basic_string/modifiers/assign/char/ move_assign.cc: Check for non-throwing exception specification. * testsuite/21_strings/basic_string/modifiers/assign/wchar_t/ move_assign.cc: Likewise. Modified: trunk/libstdc++-v3/ChangeLog trunk/libstdc++-v3/include/bits/basic_string.h trunk/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/char/move_assign.cc trunk/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/assign/wchar_t/move_assign.cc